<template>
  <div class="music-list">
    <div class="back" @click="back">
      <i class="icon-back"></i>
    </div>
    <h1 class="title">{{ title }}</h1>
    <div class="bg-image" :style="bgStyle" ref="bgImage">
        <div class="play-wrapper">
            <div ref="playBtn" v-show="songs.length > 0" class="play" @click="random">
                <i class="icon-play"></i>
                <span class="text">随机播放全部</span>
            </div>
        </div>
        <div class="filter" ref="filter"></div>
    </div>
    <div class="bg-layer" ref="layer"></div>
    <scroll :probe-type="probeType" :listen-scroll="listenScroll" :data="songs" @scroll="scroll" class="list" ref="list">
        <div class="song-list-wrapper">
            <song-list @select="selectItem" :songs="songs" :rank='rank'></song-list>
        </div>
        <div v-show="!songs.length" class="loading-container">
            <loading></loading>
        </div>
    </scroll>
  </div>
</template>

<script>
import Scroll from '../../base/scroll/scroll'
import Loading from '../../base/loading/loading'
import SongList from '../../base/song-list/song-list'
import { prefixStyle } from '../../common/js/dom'
import { playlistMixin } from '../../common/js/mixin'
import {mapActions} from 'vuex'

const RESERVED_HEIGHT = 40
const transform = prefixStyle('transform')
//  backdrop-filter 为一个元素后面区域添加图形效果（如模糊或颜色偏移）。因为它适用于元素背后的所有元素，为了看到效果，必须使元素或其背景至少部分透明
const backdrop = prefixStyle('backdrop-filter')
export default {
  mixins: [playlistMixin],
  props: {
    bgImage: {
      type: String,
      default: "",
    },
    songs: {
      type: Array,
      default: () => [],
    },
    title: {
      type: String,
      default: "",
    },
    rank: {
        type: Boolean,
        default: false
    }
  },
  components: {
      Scroll,
      Loading,
      SongList
  },
  data() {
    return {
        scrollY: 0
    };
  },
  computed: {
    bgStyle() {
      return `background-image: url(${this.bgImage})`;
    },
  },
  watch: {
      scrollY(newVal) {
          // Math.max 获取最小值 
          let translateY = Math.max(this.minTransalteY, newVal)
          let scale = 1
          let zIndex = 0
          let blur = 0
          // Math.abs 获取数据的绝对值
          const percent = Math.abs(newVal / this.imageHeight)
          if (newVal > 0) {
              scale = 1 + percent
              zIndex = 10
          } else {
            //   获取最大值
              blur = Math.min(20, percent * 20)
          }
          // this.$refs.name 获取元素   
          this.$refs.layer.style[transform] = `translate3d(0, ${translateY}px, 0)`
          this.$refs.filter.style[backdrop] = `blur(${blur}px)`
          if(newVal < this.minTransalteY) {
              zIndex = 10
              this.$refs.bgImage.style.paddingTop = 0
              this.$refs.bgImage.style.height = `${RESERVED_HEIGHT}px`
              this.$refs.playBtn.style.display = 'none'
          } else {
              this.$refs.bgImage.style.paddingTop = '70%'
              this.$refs.bgImage.style.height = 0
              this.$refs.playBtn.style.display = ''
          }
          this.$refs.bgImage.style[transform] = `scale(${scale})`
          this.$refs.bgImage.style.zIndex = zIndex
      }
  },
  created() {
      this.probeType = 3
      this.listenScroll = true
  },
  mounted() {
      this.imageHeight = this.$refs.bgImage.clientHeight
      this.minTransalteY = -this.imageHeight + RESERVED_HEIGHT
      this.$refs.list.$el.style.top = `${this.imageHeight}px`
  },
  methods: {
    handlePlaylist(playlist) {
        const bottom = playlist.length > 0 ? '60px' : ''
        this.$refs.list.$el.style.bottom = bottom
        this.$refs.list.refresh()
    },
    back() {
      this.$router.back();
    },
    scroll(pos) {
        this.scrollY = pos.y
    },
    random() {
        this.randomPlay({
            list: this.songs
        })
    },
    selectItem(item, index) {
        this.selectPlay({
            list: this.songs,
            index
        })
    },
    ...mapActions([
        'selectPlay',
        'randomPlay'
    ])
  },
};
</script>
<style lang="scss" scoped>
@import "../../common/scss/variable.scss";
@import "../../common/scss/mixin.scss";

.music-list {
  position: fixed;
  z-index: 100;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: $color-background;
  .back {
    position: absolute;
    top: 0;
    left: 0;
    z-index: 50;
    .icon-back {
      display: block;
      padding: 10px;
      font-size: $font-size-large-x;
      color: $color-theme;
    }
  }
  .title {
    position: absolute;
    top: 0;
    left: 10%;
    z-index: 40;
    width: 80%;
    text-align: center;
    line-height: 40px;
    font-size: $font-size-large;
    color: $color-text;
  }
  .bg-image {
    position: relative;
    width: 100%;
    height: 0;
    // z-index: 999;
    padding-top: 70%;
    transform-origin: top;
    background-size: cover;
    .play-wrapper {
        position: absolute;
        bottom: 20px;
        z-index: 50;
        width: 100%;
        .play {
            box-sizing: border-box;
            width: 135px;
            padding: 7px 0;
            margin: 0 auto;
            text-align: center;
            border: 1px solid $color-theme;
            color: $color-theme;
            border-radius: 100px;
            font-size: 0;
            .icon-play {
                display: inline-block;
                vertical-align: middle;
                margin-right: 6px;
                font-size: $font-size-medium-x;
            }
            .text {
                display: inline-block;
                vertical-align: middle;
                font-size: $font-size-small;
            }
        }
    }
    .filter {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background: rgba(7, 17, 27, 0.4);
    }
  }
  .bg-layer {
      position: relative;
      height: 100%;
      background: $color-background;
  }
  .list {
      position: fixed;
      top: 0;
      bottom: 0;
      width: 100%;
      background: $color-background;
      .song-list-wrapper {
          padding: 20px 30px;
      }
      .loading-container {
          position: absolute;
          width: 100%;
          top: 50%;
          transform: translateY(-50%);
      }
  }
}
</style>
